So here is a disassembly of the ftrace functions:

0xffffffff8183026b <ftrace_caller_op_ptr+7>:    mov    $0x0,%rcx
0xffffffff81830272 <ftrace_call>:       callq  0xffffffff81156d80 
<function_trace_call>
0xffffffff81830277 <ftrace_call+5>:     mov    0x40(%rsp),%r9
0xffffffff8183027c <ftrace_call+10>:    mov    0x48(%rsp),%r8
0xffffffff81830281 <ftrace_call+15>:    mov    0x70(%rsp),%rdi
0xffffffff81830286 <ftrace_call+20>:    mov    0x68(%rsp),%rsi
0xffffffff8183028b <ftrace_call+25>:    mov    0x60(%rsp),%rdx
0xffffffff81830290 <ftrace_call+30>:    mov    0x58(%rsp),%rcx
0xffffffff81830295 <ftrace_call+35>:    mov    0x50(%rsp),%rax
0xffffffff8183029a <ftrace_call+40>:    mov    0x20(%rsp),%rbp
0xffffffff8183029f <ftrace_call+45>:    add    $0xd0,%rsp
0xffffffff818302a6 <ftrace_caller_end>: jmpq   0xffffffff818302a8 <ftrace_stub>

And here is disassembly of ftrace_stub, which clearly looks broken: 
crash> dis ftrace_stub 10
0xffffffff818302a8 <ftrace_stub>:       (bad)  
0xffffffff818302a9 <ftrace_stub+1>:     (bad)  
0xffffffff818302aa <ftrace_stub+2>:     incl   0x0(%rax)
0xffffffff818302b0 <ftrace_regs_caller>:        pushfq 
0xffffffff818302b1 <ftrace_regs_caller+1>:      push   %rbp
0xffffffff818302b2 <ftrace_regs_caller+2>:      pushq  0x18(%rsp)
0xffffffff818302b6 <ftrace_regs_caller+6>:      push   %rbp
0xffffffff818302b7 <ftrace_regs_caller+7>:      mov    %rsp,%rbp
0xffffffff818302ba <ftrace_regs_caller+10>:     pushq  0x20(%rsp)
0xffffffff818302be <ftrace_regs_caller+14>:     push   %rbp

crash> rd 0xffffffff818302a8
ffffffff818302a8:  0000000080ffffff

So I guess the reason is that ftrace_stub somehow gets corrupted.

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https://bugs.launchpad.net/bugs/1605843

Title:
  Kernel crashes from time to time when using ftrace

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